I built this for my consultant/test engineering job. It's pretty simple to throw together, minus hooking all the leads from the bus bars into the relay itself inside of the enclosure (solid core wire!), but still.
Recommendations: use wood screws to secure the enclosure box and the duplex outlet boxes to the plywood board.
SainSmart 16-Channel 12V Relay Module for PIC ARM AVR DSP Arduino MSP430 TTL Logic
Uses 12VDC, 500 mA
½"x30"x48” plywood board
Should not have finish on it, you can get the cheap stuff if you want
Bus bar terminals
For securing your circuits in the box
⅛"x3"x5" aluminum mounting plates
This is what I used; ideally you'd want a plate that fits the inside of the enclosure box.
Get an indoor one at least 12"x18"x6", or larger in any dimensions that seem suitable - also, make sure to get one with holes or a grate of some kind in order to let heat escape.